Method of making single leaf springs



Sept. 2, 1952 R. SCHILLING 2,608,752

METHOD OF MAKING SINGLE LEAF SPRINGS Filed NOV. 15, 1947 2 SHEETSSHEET lA6352 5 flak/Jaw] an WIW G0 rornegs R. SCHILLING METHOD OF MAKING SINGLELEAF SPRINGS Sept. 2, 1952 2 SHEETS-SHEET 2 Filed NOV. 13, 1947 Zhwentor@iq/ iii/4', W 'u/ (Ittornegs Patented Sept. 2, 1952 METHODUFM'AKINGSINGLEIEAFSPRING'S Robert Schilling; 'Birmingham 'MiclL, assignct to"General Motors" Corporation, netroih Mic'hl a cnrporation of DelawareApplibatibn November, 13; 1947, seriarivorvss vts" 16 Claims. (Cl.29-173') :1"v Y 'TYiis inventionJreIetes generally to springs an i'thelmanufecture thereoflandji's more particularly concerned withl'eafis-prings .an'd thet p'roc essing thereof.

Conventional leafsprings are laminated and consist of a piuralityofhl'ades. fIn coritra'stgthe leaifv spring ofthe presentlinvention ismade out oifasingiebiade:

order to arrive at a; minimum weighte Iea'f sprfi-igmustloedes'ignedso'that' the operating stresses are the same ateupoints;Consequently a, single leaf spring must then have either a variablewidth, a variable thickness or both. 'A studyofithese possibflitieshasshown that a single l'eaf' spr'ingi w01 substantially constant widthand, with e. variable thicknessis most practicable. The.pre'ferredi'form of. Single l'eafsnringJin eccordance with"thisinventiontherefore is of .constant o'rsuostantially constant widthand varies in'tnickr' jessffrom a'maximum' at the center toua minimumatlipoints' adjacentthe two ends thereof; fit nas'a oout the semelengthand width as e conventional laminated spring but is much thinner; Thedesign ibeoomeypossibl'e because novefprocessing permitslth'e use of.much jliigher operating stressestlianis"present practice;

The cross section ofthespring blade of the invention may take" various"forms, Ordinarily it i's'of rectangular cross section with slightlyrounded edges ('COIHGY" radius" i 'to inch). However; special: sectionssuch as" center groove or paraboli'c edgesarealso possible; V

The single leaf spring of this invention "is espeoiallywelisuit'edforrear suspensions of ijpas senger' ears; It'Tllay'b'e used" also for"front; suspensions although it does not show somany-edvant'agesin'suchinstances;

The"fasteningstotheaxle'end'chassis-aresimilar *to" those :empl'oye'dwith conventional' lami natedsprings: -It ispreferred not'to' useadirect meta l to 'metal :olamp' atthe' spring center, because 'suchi'aclamp causes a certain amount of clia'fing which may lead to "failures"at the high stressesused. A liner offl'exible or plastic materialis-used between'the sprineblede endiciamp; to insure unif'ormsurfacepressures andfprevent chafing. '-It is-preferred-also to avoid-theconventionai oenter bolt'hoie, and toiuse instead 2; pair 0f grooves a'tthe-side of the spring at the neutralaxis for the purpose of centering:the spring 'gintitaking longitudinal loads. Itis 1pos= sible to omitthe grooves tend locate the spring by cementing it'totherirbberseatioads;

one important advantage of "the-single leaf spring of -'thisinvention-:compared with" a laminated'lea-f spring; is its -greatlyfreduoedweight. This is brought about-by theincre'ased' operating infull linesandthe'maximum gload position stress and the'redu'cti' n "of inectivespfingimae teriai'. The manufacturing cost-is reduced in proportiontothelower raiwmaterial weightrand to'th'e'smell'er number of partsto-beprooessedi In operation an important advantage-751s tileelimination of static friction of 'laminatedfleaf springs; Spring coversor liners'are not-needed and the spring requires no servicing; The-ridedoies not change because the 'veriable frietion nolonger'present. l

The'primary' objects of'the invention are-to provide-asingle leaf'springhaving'the edvanteges outlined above andto provide? an improved method'or' methods of processing I such spring; Another object is 'to'p'rovideran im-proved step or steps in a method of spring processing-which isapplicable also tootherspringsthan single leaf springs; Other obj eetsand eidvan te'gesQof the invention will :bee-ppetrent from thedescriptieri which-follows; 5 Reference -isjiierewlth mad'e to' theaccompany ing= drawingsillustraiting ai-single leaf spring-=arid theprocessing-thereof in accord' ance witli-e' p rf ferred-em'bodiment oftheinventionn Inthe drawings: v i 3 I Figure 1-is a=view' illustratingthe*-step of of; rolling a steel springblank of substantiallyauniformwidthand-of avariabletliiokness. 1 Figurefl'illustratesthe step offor-m'i-ngtli eyes on-the; ends of the'springhlank off Figur Figure 3il1ustrates: the step of quenching the spring on acurved-fixture in thehardening opelation. 7

Figure-4 illustrates the sho't peeriing of a lieet treat'edspri'ng whilethe spring 'i's under 1mm; Figure 5- is a; diagrammatic view of theidjdl contour of a semi-elliptic springof uni form width 'eind va'riablethickness having uniform op eratingstresse's-at all sections', thespring thi'c ness' being shownon ailargersettlethemis tlie length. 1'

Figure 'fi is a diagrammatic view; showing a; m'odificaition oftheideal-contbur of Figure- 5} the spring" thickness being shown-on a;ilaii'ger scale than "is the length.- Figure 7 showsone form ofappartus'wviiili' is used for prestressingthe-spring after itih'azs beensliot-peened. 'i

fi ed s tes a l rros o 1 sistan-t coating to "protest thespring fiomi'o'or;

rosl'onin-service; V I I Figure 9 isjiwcomposit'e view ofthetdifferentpositionsor shapes of tli-e spring at difie' rent points-in theprocessing'andyor operatingioycles; Figure 10 is-a view sliowingthespring'installefdj the-static'load position'of the "spring being theunloaded position being shown in dotted lines.

In forming the single leaf spring, steel or other spring material is hotformed as by rolling or otherwise into the required shape such that theoperating stress will be the same or substantially the same at allsections. In Figure 1 is.diagrammatically shown the operation of hotrolling a spring blank [0. The blank shown is of constant width and ofvariable thickness with the portion of maximum thickness at the centerof the blank where the spring will be attached to the axle. The bottomface of the spring blank is fiat and the upper face is of a contour suchthat the operating stresses will be substantially equal at all sections.

The ideal contour of a semi-elliptic spring of constant width havinguniform operating stresses at all sections is diagrammatically shown inFigure 5. The bottom face H is fiat and the upper face is formed of twoparabolic contours l2 and I3. Figure 6 shows diagrammatically the mannerin which the ideal contour of Figure 5 is modified in the designillustrated in the several drawings herein.- 'At the center the twoparabolas of Figure 5 are faired by a circular arc H which slightlyreduces the thickness within the spring length which will be clamped bythe center clamp. At the ends l5, I5 the thickness is held constant at aminimum value in order to provide sumcient stock to form eyes. InFigures 5 and 6 the thickness of the spring is shown on an enlargedscale as compared with the spring length in order to illustrate moreclearly the contour or the single leaf spring.

The rolling operation may be carried out in any desired way. Forexample, the rolling may be accomplished in a single pass and incontinuous strip form at the steel mill. Thisinay be done at the lastpass of the strip rolling process, so that no separate heating isrequired. The rolllng also may be carried out in a number of successivepasses in a manner analogous to the taper rolling on blades forlaminated springs. V

Figure 2 illustrates the step of eye forming. This step is similar tothat on the main leaf oi? laminated springs. The eyes are shown at [8.

After forming the eyes the blade is heat treated. In this operation thespring steel blade is heated to a hardening temperature above AC3. It isthen mounted on a quench form such as shown in Figure 3 so shaped as toimpart a desired curvature to the heated spring. The fixture showncomprises a lower portion l-l and an upper portion I8 between which theheated spring is held. It is then quenched with oil or by other suitablemeans to harden the spring. The quench form is designed to allow forchanges in shape during subsequent processing steps so that the springwill have the desired shape and standing height in service. The hardenedspring is then removed from the quench form and tempered withoutrestraint. This operation consists in reheating the hardened spring to aspring tempering temperature considerably lower than that employed inthe hardening operation. The tempering treatment does not change thecurved shape of the spring resulting from quenching the spring in thecurved fixture. The hardening and tempering temperatures may be the sameas those employed in heat treating conventional springs. As a specificexample of heat treatment, the spring may be heated to 1600 F. and heldat this temperature for about two hours. It is then quenched in oil toharden the same. It is thereafter reheated to a tempering temperature onthe 4 order of 750-920 F., the lower tempering temperatures beingemployed with steel of lower carbon content and the higher temperatureswith spring steel of higher carbon content.

After being hardened and tempered the single blade is shct-peened whileunder load. The spring blade which is curved when free, is clamped to aform or fixture so that it is approximately fiat and under a stressbetween 125,000 and 200,000 lbs. per square inch (mostly about 175,000lbs. per square inch) with the tension side exposed. In general theshot-peening is carried out while the spring is loaded in the directionof service loading to a tensile stress on the order of about 60% to ofits yield point. The shot-peening is carried out by causing hardenedsteel shot to impinge upon the tension surface of the spring blade. Theshot may be directed by a high velocity air stream against the tensionsurface, or the shot may be thrown from the periphery of a wheel whichis rotating at high speed and caused to impinge upon the tensionsurface. The spring is passed through the shot-peening machine so thatthe entire tension side isthoroughly shot-peened. Best results areobtained when the corners adjacent the tensile side are also shotpeened.The shot are caused to travel at such high speed that they effect a coldworking of the spring surfaces contacted thereby. Since the spring isalready stressed near to its yield point the effect of the peening ismore severe and penetrates more deeply than it would on an unstressedspring, The peening greatly improves the load carrying capacity and theendurance of the spring. At the same time the spring takes aconsiderable set during peening which must be allowed for when designingthe quench form. One means for carrying out the shot-peening operationon the tension side of the spring is illustrated in Figure 4. In thisfigure, 20 represents a form to which the spring is clamped by means ofsimilar clamps 22. Shot-peening nozzles are shown at 24. For peening thecorners adjacent the tension side, the nozzle or nozzles may be arrangedat an angle; for example, very efiective peening is obtained when thenozzles are at an angle of 45 to the vertical. The peening operation maybe carried out in one or more passes through the machine. So far as I amaware, the operation of shot-peening while under load, is novel per se.It can beused also in treating other springs than single leaf springs inorder to improve greatly the endurance and load carrying capacitythereof.

After the shot-peening operation the single leaf spring is preset bydeflecting it in the directionof service loading without application ofheat by an amount which is in excess of the maximum service deflectionby between ten and thirty per cent. During presetting the spring takes afurther set which also must be considered and taken into account indesigning the quench form. The presetting accomplishes two main purpose(1) it minimizes subsequent settling in serviee and (2) it allows areadjustment of standing height, so that variations due to material andprocessing can be corrected. One form of apparatus for carrying out thepresetting operation is illustrated in Figure 7. In this figure, 30represents a form against which the spring is deflected by loading means32. The presetting also may be performed by clamping the blade betweenmale and female terms, or simply by loading it with a load which 1s inexcess of the maximum service load by between ten and thirty per cent.

After presetting the spring has the correct free shape, which shows lesscurvature than that of the quench form.

The spring preferably is coated after presettmg with an anticorrosioncoating, such as one of the hosphate treatments (Parkerizing,bonderizing) or painting. The coating operation is illustrated in Figure8 in which the spring i shown immersed in a coating solution 38 in atank 38.

Figure 9 is a view showing the various shapes of the spring duringprocessing and operating superimposed. In this figure A illustrates theshape after hardening and tempering, B illustrates the shape aftershot-peening, C represents the free shape of the finished spring, Drepresents the approximate shape at static load, E represents the shapeat maximum service load and F represents the shape to which the springis preset. The difference between shapes A and B is that due to theshot-peeping, and the difference between shapes B and C is the set dueto presetting. The operating range extends from the free shape of thefinished spring (shape C) to the shape at maximum load (position E). Thedifference between the shape at maximum load (position E) and the shapeto which preset (position F) is the margin by which presetting exceedsthe maximum operating deflection.

Figure 10 illustrates the single leaf spring as installed, The ends ofthe spring are shown connected to the chassis 48 in the same generalmanner as conventional laminated leaf springs. The center of the springis clamped by the clamp 59 to axle 52. The full line position of thespring shows it in its static load position. The upper broken lineposition is the maximum load position, while the lower broken line isthe unloaded position.

Load capacity and endurance of a spring may be increased if theshot-peening operation is repeated after the presetting of the spring.This can be done with a spring in the free shape condition or in astressed condition asshown in Figure 4. Best results have been obtainedwhen during the second shot-peening operation the spring was held underapproximately the same stress as in the first shot-peening operation.The additional settling of the spring during this operation must also beallowed for in the quenched shape of the spring.

While I have shown what I consider to be a preferred embodiment of myinvention, it will be understood that various modifications andrearrangements may be made therein without departing from the spirit andscope of the invention.

I claim:

1. The method of making a. single leaf spring characterized by high loadcarrying capacity and endurance which comprises providing a hardened andtempered steel leaf spring of substantially uniform width and ofvariable thickness ranging from a maximum at a point substantiallymidway between the ends to a minimum adjacent each end, flexing saidleaf spring to produce a tensile stress on the order of 60% to 100% ofits yield point on the tension side of said leaf spring; shotpeening thetension side and adjacent corners of said leaf spring while it is undersaid tensile stress and then presetting said leaf spring by de fleetingit in excess of maximum service deflection by between ten and thirty percent.

2. The method of making a single leaf spring characterized by high loadcarrying capacity and endurance whichcomprises, providing a hardened andtempered steel leaf spring, loading said leaf spring to produce atensile stress on the order of 125,000 to 200,000 pounds per square inchon the tension side of said leaf spring, shot-peenlng the tension sideof said leaf spring while it is under said tensile stress andsubsequently presetting said leaf spring by deflecting it in excess ofthe maximum service deflection by between ten and thirty per cent.

3. The method of making a single leaf spring characterized by high loadcarrying capacity and endurance which comprises, providing a hardenedand tempered steel spring blade of substantially uniform width and ofvariable thickness ranging from a maximum at a point substantiallymidway between the, ends to a minimum adjacent each end, flexing saidspring blade to produce a tensile stress on the order of 60% to of itsyield point on the tension side of said spring blade and shot-peeningthe tension side and adjacent corners of the spring blade while it isunder said tensile stress.

4. The method of treating spring which comprises shot-peening a steelspring while it is loaded in the direction of service loading to atensile stress on the order of 60% to of its yield point.

5. A method as in claim 1 in which the spring also is subjected to ashot-peening operation after the presetting of the spring.

6. The method of making a single leaf spring characterized by high loadcarrying capacity and endurance which comprises hot forming steel into asingle leaf spring of substantially uniform width and of variablethickness ranging from a maxmum at a point substantially midway betweenthe ends to a minimum adjacent each end whereby said steel spring willhave substantially uniform operating stresses at all sections, heatingsaid steel spring to a hardening temperature, quenching said heatedsteel spring to harden the same while the spring is held in a fixture toimpart a curvature thereto, reheating the hardened and curved leafspring to a tempering temperature, flexing said leaf spring to produce atensile stress on the order of 60% to 100% of its yield point on thetension side of said leaf spring then shot-peening the tension side andadjacent corners of said leaf spring while it is under said tensilestress, andthereafter presetting said leaf spring by deflecting it inexcess of maximum service deflection by between ten and thirty per cent.

ROBERT SCHILLING.

REFERENCES CITED The following references are of record in th file ofthis patent:

UNITED STATES PATENTS Numb er August 1945, pages l41-149.

